The question "IPv6 link-local addresses for virtual interfaces are identical - how to assign “link-unique”? " has been put on hold as offtopic on NE. Help page "What topics can I ask about here?" explicitly lists this as on-topic:
[...] On-topic: Questions about Unix / Linux Servers which are running Network Protocols or a Firewall Questions about firewalling or network protocols such as OSPF running on linux / unix servers.
This is exactly what the question is about. It asks "What is the right way to obtain IPv6 addresses, which would be unique on the link, for such [VPN] interfaces?", pointing that this is needed for proper functioning of OSPFv3 on a Linux server.
How is this question not suitable for NE?